Antoni Sarcevic scored on his first Plymouth start to earn a 1-0 win at Cambridge.
The Pilgrims had to survive an early U's onslaught, with Ben Williamson's goal-bound header deflected wide and debutant Liam O'Neil's shot looping onto the top of the bar.
At the other end both Sarcevic and Matthew Kennedy were denied by excellent Will Norris saves and Graham Carey headed over from Kennedy's cross.
They were ahead four minutes before half-time when Sarcevic powered a header into the corner following Carey's cross.
Cambridge could have been level on the stroke of half-time when Carey's clearance on the line kept out Scott Wharton's header from Piero Mingoia's corner.
The home side pressed hard in the second half, with Luke McCormick called upon 20 minutes from the end to parry away Paul Lewis' header moments after the midfielder had arrived from the bench.
They almost drew level nine minutes from the end when Wharton was again denied from a corner, seeing his header cleared off the line by David Fox.